The invention relates to the field of BST microwave tunable devices, and in particular to an integrated BST microwave tunable device using a buffer layer transfer method.
(Ba,Sr)TiO3 (BST), (Ba,Zr)TiO3 (BZT) (Ba,Hf)TiO3 (BHT), SrTiO3 (ST), Bi1.5Zn1.0Nb1.5O7 (BZN series, B:Bi, Ba) and related thin films are promising materials for tunable microwave devices application such as electronically tunable mixers, oscillators, and phase shifters and filters. It will be appreciated by those of skill in the art that BST is representative of one or more related perovskite-like tunable dielectric materials.
An objective of the invention is to integrate tunable components into monolithic microwave integrated circuits (MMICs). Although microstrip planes are the most common transmission line component for microwave frequencies, the ground-plane is difficult to access for shunt connections necessary for active devices, when used in MMICs. The CPW (Coplanar Waveguide) is an attractive alternative, especially due to the ease of monolithic integration, as the ground plane runs adjacent to the transmission line. The possibility of creating BST microwave tunable devices on oxide substrates has been demonstrated in recent years. There is a great incentive to replicate these achievements on silicon-based wafers for integrated microwave device applications.
Much work has been done to obtain epitaxially grown ferroelectric thin films on Si substrates. Currently, chemical vapor deposition methods such as MBE (Molecular Beam Epitaxy) and ALD (Atomic Layer Deposition) and as well as physical vapor deposition methods such as pulsed laser deposition have been used. However, it has not been easy to obtain high quality buffer films without residual stress and defects resulting from a dimensional misfit between the crystal lattices.